They were more than angry, those days when Adolf Hitler devastated Europe while America fretted about non-intervention.

As British Prime Minister Winston Churchill struggled to persuade American President Franklin Roosevelt of the global stakes involved in a German victory, Americans grappled with decisions that tested their courage and would ultimately transform their nation into a superpower.

Lurking in the wings of Lynne Olson’s panoramic account of the savagely isolationist politics of America in years leading up to World War II is the bizarre figure of Charles Lindbergh, the national hero who became a national controversy. She uses him like a bookend, sandwiching his hysterical opposition to American intervention between his initial heroism and the stunning postwar revelation that this moral icon fathered seven children by three German women.

Perhaps too much of “Those Angry Days” is devoted to the awful Lindbergh and not enough to the indecisiveness of Roosevelt. However, this is a solidly researched history of how America fought its way out of isolationism after being split between multiple factions, notably during the mudslinging of the 1940 presidential election between Roosevelt and Wendell Willkie — all this taking place while the Nazis straddled Europe and the British endured the London blitz with its thousands of civilian casualties. Perhaps that is why Ms. Olson’s previous books about World War II as experienced in Britain — “Citizens of London” and “Those Troublesome Young Men” — bore more of a sense of immediacy and poignancy. They imprinted a human face on war, turned personalities into people and brought into focus the politics of a fading empire.

Her current work is a more impersonal portrayal of American politics, in which an astonishing number of politicians are either crippled by warped vision or have no sense of a potentially terrifying future. Reality struck only when the Japanese included the United States in the path of slaughter it was pursuing to build a Far Eastern empire.

Not even Lindbergh could defend the attack on Pearl Harbor, but he never admitted he was wrong about the need for Americans to become involved in World War II. It would seem that Lindbergh has received far more attention than his famous flight merited. His grief over the murder of his infant son is understandable, but there is no explanation for his boneheaded refusal to comprehend the potential reach of Nazi power. It is remarkable that his sensitive and intelligent wife did not flee her marriage to such a man.

Ms. Olson points out that Lindbergh had the gall to equate the Nazis’ wholesale murder of the Jews with crimes committed by American troops against Japanese prisoners of war. Unlike his wife, the author adds, Lindbergh uttered “no word of remorse or apology for his uncritical attitude toward the horrors of Hitler’s regime.”

It is a relief when Ms. Olson turns her attention to the cadre of strong men who emerged to help lead America out of the political mire of the America Firsters and the frustration of Roosevelt’s capacity for indecision. She cites men such as Gen. George C. Marshall and Henry Stimson, a Republican who became secretary of war and a staunch defender of American intervention in the war. Stimson was one of those who was never afraid to speak his mind whatever the political consequences. Willkie lost his bid against Roosevelt and immediately rushed to support an American stand against Hitler. Lord Philip Lothian, whom Roosevelt called the best British ambassador he ever knew, fought so desperate a battle to engage America in war that he destroyed his health and died an early death. It was Lothian who had the diplomatic courage to tell the press, “Well, boys, Britain’s broke. It’s your money we want.”

It was then, when the future of the crucial Lend-Lease plan was in the balance, that Churchill sent Roosevelt a blunt warning: “There is only one duty, only one safe course, and that is to try to be right and not to fear to do or say what you believe to be right.”

Playwright Robert Sherwood, who raged constantly against American lethargy, asserted that in America was seen “the awful picture of a great nation which had surrendered all powers of initiative and therefore must wait in a state of flabby impotence for its potential enemies to decide where, when and how action would be taken.”

Ms. Olson also makes the harsh charge that had Hitler not decided to go to war against America, “the odds are high that Congress and the American people would have pressured the president to turn away from an undeclared war against Germany and focus instead on defeating Japan. American shipments of arms to Britain and Russia might have been cut dramatically or even halted, and Germany would have had a clear shot at defeating both countries.”

The brutal truth is that she could well be right. In many respects, this is a look back into political darkness.

Muriel Dobbin is a former White House and national political reporter for McClatchy newspapers and the Baltimore Sun.